In the backdrop of ever dwindling fossil fuel resources, researchers are exploring ways of harnessing alternate sources of energy. Solar energy is a promising alternate source of energy. Engineers are facing several challenges in capturing, storing and converting solar energy. The problem of converting solar energy into electricity in a cost-effective manner and on a large scale still poses challenges.
Several approaches are being followed to reach the goal of generating a large-scale and reliable flow of electricity from solar energy. One such method is through the use of a solar central receiver mounted on top of a tower. The solar receiver is basically a heat exchanger that absorbs concentrated solar energy. The receiver absorbs the sun's energy in a concentrated form from an array of mirrors called heliostats. The receiver comprises a number of panels. Mounted on the panels is a connected set of tubes carrying a heat absorbing fluid. The fluid inside the tubes traces a serpentine path from panel to panel when circulating inside the tubes. The receiver functions as a heat exchanger to transfer the solar energy received from the heliostats to the heat absorbing fluid carried by the tubes. For example, in one design molten salt is pumped up to the receiver and circulated inside the receiver panel tubes. The molten salt is heated by the solar energy absorbed by the receiver tubes. The heated molten salt flows into a ground based hot thermal storage tank(s). Hot molten salt is then pumped from the hot thermal storage tank as needed to create steam that powers a steam turbine for generating electricity.
Panels are comprised primarily of a strongback, insulation, receiver tubes, headers and tube guide/supports. Tubes are connected at the top and bottom of the panel by the headers. The tube-header assembly is connected to the guide/supports by clips. The guide/supports are rigidly attached (welded or bolted) to the strongback, which in turn is attached to the receiver tower super-structure. In known receiver designs, though multiple clips may be used to hold the tubes, it is the topmost clip which bears the vertical deadweight of the tubes and header assembly. Other clips along the tube length carry the horizontal and bowing loads on the tubes and also maintain the alignment of the tubes. Thus, the known receiver designs use a top supported panel design where the vertical load of each tube is carried solely by the topmost clip at an upper end of each tube.
The top supported receiver panel design, while having proven to be effective, could nevertheless be improved in several ways. Since the tubes are supported at the top, as the tubes thermally expand, they expand in a downward direction when thermal flux is applied. Top supported receiver panels generally also require relatively large cold supply and hot return pipelines for molten salt to be attached near the top of the receiver panel that is stationary during changes in temperature. Consequently, the top supported receiver panels all require relatively large pipelines to be run through the congested center of the cylindrical receiver and to the tops of the panels. This arrangement also requires lengthy pipe runs. Therefore, construction can often become complex due to the routing difficulties and lengthier pipes used within the cylindrical receiver. Even a flat billboard shape receiver requires long runs of large pipe if the panels are top supported.